The present invention relates to a process control terminal, and more particularly to a process control terminal having the capability to simultaneously display process control information and other unrelated information in mutually exclusive portions of a display screen.
The field of process control relates to the interactive control of complicated processes such as chemical processes used in chemical and oil refineries, processes used in food processing, processes used in pulp and paper producing plants, etc. The typical variables that need to be controlled during such processes include temperatures, pressures, flow rates, and quantities.
In order to monitor and control such processes, process control networks are typically used. Such a network includes a number of process control terminals connected to a plurality of process controllers which monitor the processes. The process control terminals are monitored closely by operators, who may be required to respond quickly to visual alarm messages on the process control terminal screens. Such alarm messages may indicate dangerous or undesirable conditions, such as a dangerously high pressure or a temperature that is out of range, which could result in damage to the process control facility, such as rupture of a conduit or boiler, or in defective product.
The operator is also be required to respond to attention messages generated on the process control terminal screens. Such an attention message indicates the need for the operator to take a particular action, depending upon the particular message. For example, the supply of a chemical used in a process may be low. In this case, the process controller monitoring the supply of the chemical would transmit an electronic low supply message to the appropriate process control terminal, which would then show the corresponding visual message on the screen. The operator, upon seeing the message, would make sure that the particular chemical supply would be refilled.
When monitoring a process control terminal, an operator typically experiences relatively extended periods of time during which no alarm or attention messages are generated. As a result, the operator has nothing to do. Not only is this lack of duties an inefficient utilization of the operator's time, but the operator may become bored. One approach to remedying this problem might be to provide the operator with a separate computer and display screen so that the operator could perform additional tasks during his spare time. However, this approach suffers the drawback that another display screen and computer are required, resulting in the need for extra space as well as cost.
One general approach to a similar problem is described in U.S. Pat. No. 4,761,642 to Huntzinger. Huntzinger discloses a computer system which has the capability of simultaneously responding to multiple application programs being executed by a host computer. A single display terminal is connected to the computer system, and a window is shown for each active application program being executed by the host computer. The Huntzinger system has serious disadvantages in the context of process control terminals. One using the Huntzinger system may hide windows from view by "burying" one window behind another window so that portions of the buried window do not appear on the screen. Furthermore, the user may "collapse" a window, which causes the entire window to disappear from the screen, the only remnant of the collapsed window being a small icon displayed along the edge of the screen.
If used in a process control system, the Huntzinger system could have disastrous consequences. If the operator were to partially obscure one or more windows relating to process control, the operator might miss alarm or attention messages, which could result in damage to the process control facility or defective product. Moreover, the application of the Huntzinger system to the process control area would defeat the operator's primary responsibility, that of monitoring the process.